Ok, firstly, I haven't used Ubuntu for some time, so while this information might be only *partly* accurate, I'll try to point you to the correct HELP pages where necessary.
1 - For information on putting encoding flags in /etc/fstab, go in a console and type 'man fstab' and 'man mount'. These are help pages. The 'mount' halp page has all the possible options you can use when mounting media. Before going crazy editing the fstab file, your best bet will be to use the mount command in a console and experiment with it. A typical mount command is like:
mount -t iso9660 /dev/hdc /mnt/some-folder -o ro utf8
..that command would try to mount an iso9660-formatted CD in device HDC, on the mountpoint /mnt/some-folder, with options 'read-only' and character-set encoding UTF8.
The UTF8 part is where you would play around and see if another character-set would enable you to mount a CD with different character encodings.
Taking a guess, the method you used to add Cyrillic/Russian support is fine for reading/writing text, webpages, desktop stuff etc., but *might* not be enough for the disk drives and kernel to deal with Russian characters in filenames on mounted media, or perhaps the encoding on that media is not quite the same as that for which you have no trouble reading already.. The fact that the media might have been made with Windoze is relevant, but isn't the final word -- there is likely a way around it.
If this were me, I would look into the kernel compile, and see if/any Native Language Support has been made available for the Disk/IO/Media section. If you are very new to all this, you will want to do some reading about compiling a kernel, before getting into this. There are tonnes of threads around here about compiling the kernel, and also a small readme file inside the kernel source folder. If you can't find the kernel source code on your system in /usr/src/linux/, then it *should* be on the Install CD (not sure with Ubuntu) OR you can download it from a kernel mirror yourself.
The section you specifically want to look into is 'Native Language Support', where you can compile in language code-pages which allow the I/O system to handle media with foreign language filenames.
I have Russian/Cyrillic support built into my system, by several means; here are the codepages I have used in the kernel. This may look a bit cryptic right now, but IF/when you want/need to add Languages to the Kernel, the Descriptions and instructions are quite clear, and will tell you in English what each codepage is for:
# Kernel Native Language Support
Best of success